333
FXUS61 KPBZ 151157
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
757 AM EDT Thu Aug 15 2024

.SYNOPSIS...
Dry and comfortable again today with warmer temperatures. A
low pressure system will begin to slowly cross the Great Lakes
region Friday and drift eastward into early next week. This
pattern will bring with it the risk for periodic showers and
storms.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
KEY MESSAGES:

- Dry weather continues today with warmer temperatures.

-------------------------------------------------------------------

Rising heights at 500mbs, and high pressure at the surface,
will provide another dry day with plenty of sunshine. Warm air
advection, within the eastward moving ridge, will nudge
temperatures a few degrees above normal.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
KEY MESSAGES:

- Shower/storm chances increase Friday, but timing issues still
  remain.
- The threat for rain continues into Saturday with the slow
  passage of a surface front.

-------------------------------------------------------------------

A large upper level low will drift toward the western Great
Lakes on Friday. Waves of energy, rotating around the low, will
be ejected eastward, crossing the region on Friday. The first
wave in the morning will use up most of its energy breaking
down the ridge axis which will be located over western PA. This
will bring an increase in cloud cover, but should limit the
rainfall. A second and stronger wave will cross Friday
afternoon, pulling a surface front through the area. This will
provide a higher risk for widespread shower activity. The
convective threat is still murky due to a lack of instability
and strong shear. Latest NBM data shows CAPE values less than
1000 j/kg, with much of the deterministic model data advertising
wind shear of less than 20kts. An additional hindrance to storm
development would be the increased cloud cover Friday morning
as well as the warm air advection aloft. Latest CAM models are
showing a line of storms moving across western and central OH
Friday morning, but then weakening as they move further
eastward. The CAMs are also hinting at the morning convection
diving southward into a region of higher instability and
stronger shear. The NBM keeps the higher probability for thunder
later in the day with a large chunk of those higher
numbers over Ohio. PWAT values will rapidly increase Friday, so
if stronger convection does develop, there will be the threat
for heavy rainfall.

Temperatures Friday will cool a bit, closer to seasonal
averages.

The 500mb low will continue to drift eastward on Saturday,
lowering heights even further over the region. A surface cold
front, extending south of the stacked system, will cross the
area Saturday afternoon. The risk for showers and storms will
continue Saturday, but still much to be determined. NBM is
showing a more buoyant atmosphere and deterministic models are
increasing the shear to around 30kts. So if storms can initiate
the ingredients will be in place to support stronger convection.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
KEY MESSAGES:


- Ensembles favor Great Lakes troughing into early next week
  that would maintain low probability, diurnally driven
  convection.
-------------------------------------------------------------------

Upper trough crawls east across western and central PA on
Sunday, with shower chances continuing especially over PA/WV
counties.

Ensembles indicate that long wave trough will continue to linger
in the Great Lakes and Northeast States Monday, Tuesday, and
Wednesday. The standard deviation of 500 mb heights in this area
gradually increase with time as the details of short wave
troughs become less and less evident. NBM provides low rain
chances during the period with somewhat higher values on Monday,
but confidence is low and it certainly could end up being dry
for a few days with northwest flow.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
After river valley fog diminishes by mid morning, high pressure
will maintain dry conditions today. Dry weather will continue
overnight with a lowering VFR cloud deck in advance of shortwave
troughing.

.Outlook...
VFR conditions are expected to continue into early Friday
morning before a shortwave brings chances of rain showers and
thunderstorms to the area. Probabilities of MVFR are around
10%-20% on Friday for all sites due to lowering VIS. An upper
level trough moves through on Saturday, causing showers and
occasional thunderstorms. MVFR (50%-70%) and IFR (30%-50%)
restrictions caused by low CIGs are more likely Saturday
morning, but could remain through the afternoon. Periodic
showers and thunderstorms with occasional restrictions are
possible through Monday with the slow moving trough.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.

&&

$$

SYNOPSIS...22
NEAR TERM...22/Shallenberger
SHORT TERM...22
LONG TERM...Craven
AVIATION...Rackley/88